Liquid-crystalline compounds

ABSTRACT

Liquid-crystalline compounds of the formula I 
                         
in which
         R 1 , A 1 , A 2 , Z 1 , Z 2 , X, a, b, L 1 , L 2  and L 3  are as defined herein, and to liquid-crystalline media comprising at least one compound of the formula I and to electro-optical displays containing a liquid-crystalline medium of this type.

The present invention relates to liquid-crystalline compounds and to aliquid-crystalline medium, to the use thereof for electro-opticalpurposes, and to displays containing this medium.

Liquid-crystals are used principally as dielectrics in display devices,since the optical properties of such substances can be modified by anapplied voltage. Electro-optical devices based on liquid crystals areextremely well known to the person skilled in the art and can be basedon various effects. Examples of such devices are cells having dynamicscattering, DAP (deformation of aligned phases) cells, guest/host cells,TN cells having a twisted nematic structure, STN (supertwisted nematic)cells, SBE (super-birefringence effect) cells and OMI (optical modeinterference) cells. The most common display devices are based on theSchadt-Helfrich effect and have a twisted nematic structure.

The liquid-crystal materials must have good chemical and thermalstability and good stability to electric fields and electromagneticradiation. Furthermore, the liquid-crystal materials should have lowviscosity and produce short addressing times, low threshold voltages andhigh contrast in the cells.

They should furthermore have a suitable mesophase, for example a nematicor cholesteric mesophase for the above-mentioned cells, at the usualoperating temperatures, i.e. in the broadest possible range above andbelow room temperature. Since liquid crystals are generally used asmixtures of a plurality of components, it is important that thecomponents are readily miscible with one another. Further properties,such as the electrical conductivity, the dielectric anisotropy and theoptical anisotropy, have to satisfy various requirements depending onthe cell type and area of application. For example, materials for cellshaving a twisted nematic structure should have positive dielectricanisotropy and low electrical conductivity.

For example, for matrix liquid-crystal displays with integratednon-linear elements for switching individual pixels (MLC displays),media having large positive dielectric anisotropy, broad nematic phases,relatively low birefringence, very high specific resistance, good UV andtemperature stability and low vapor pressure are desired.

Matrix liquid-crystal displays of this type are known. Non-linearelements which can be used for individual switching of the individualpixels are, for example, active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made betweentwo types:

-   -   1. MOS (metal oxide semiconductor) or other diodes on a silicon        wafer as substrate.    -   2. Thin-film transistors (TFTs) on a glass plate as substrate.

The use of single-crystal silicon as substrate material restricts thedisplay size, since even modular assembly of various part-displaysresults in problems at the joins.

In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect. A distinction ismade between two technologies: TFTs comprising compound semiconductors,such as, for example, CdSe, or TFTs based on polycrystalline oramorphous silicon. Intensive work is being carried out world-wide on thelatter technology.

The TFT matrix is applied to the inside of one glass plate of thedisplay, while the other glass plate carries the transparentcounterelectrode on its inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fully color-capabledisplays, in which a mosaic of red, green and blue filters is arrangedin such a way that a filter element is opposite each switchable pixel.

The TFT displays usually operate as TN cells with crossed polarizers intransmission and are illuminated from the back.

The term MLC displays here covers any matrix display with integratednon-linear elements, i.e., besides the active matrix, also displays withpassive elements, such as varistors or diodes(MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications(for example pocket TVs) or for high-information displays for computerapplications (laptops) and in automobile or aircraft construction.Besides problems regarding the angle dependence of the contrast and theresponse times, difficulties also arise in MLC displays due toinsufficiently high specific resistance of the liquid-crystal mixtures[TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K.,TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p.141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Designof Thin Film Transistors for Matrix Addressing of Television LiquidCrystal Displays, p. 145 ff, Paris]. With decreasing resistance, thecontrast of an MLC display deteriorates, and the problem of after-imageelimination may occur. Since the specific resistance of theliquid-crystal mixture generally drops over the life of an MLC displayowing to interaction with the interior surfaces of the display, a high(initial) resistance is very important in order to obtain acceptableservice lives. In particular in the case of low-volt mixtures, it washitherto impossible to achieve very high specific resistance values. Itis furthermore important that the specific resistance exhibits thesmallest possible increase with increasing temperature and after heatingand/or UV exposure. The low-temperature properties of the mixtures fromthe prior art are also particularly disadvantageous. It is demanded thatno crystallisation and/or smectic phases occur, even at lowtemperatures, and the temperature dependence of the viscosity is as lowas possible. The MLC displays from the prior art thus do not meettoday's requirements.

There thus continues to be a great demand for MLC displays having veryhigh specific resistance at the same time as a large working-temperaturerange, short response times even at low temperatures and low thresholdvoltage which do not have these disadvantages, or only do so to areduced extent.

In TN (Schadt-Helfrich) cells, media are desired which facilitate thefollowing advantages in the cells:

-   -   extended nematic phase range (in particular down to low        temperatures)    -   the ability to switch at extremely low temperatures (outdoor        use, automobile, avionics)    -   increased resistance to UV radiation (longer service life)    -   high Δn for faster response times

The media available from the prior art do not allow these advantages tobe achieved while simultaneously retaining the other parameters.

In the case of supertwisted (STN) cells, media are desired which enablegreater multiplexability and/or lower threshold voltages and/or broadernematic phase ranges (in particular at low temperatures). To this end, afurther widening of the available parameter latitude (clearing point,smectic-nematic transition or melting point, viscosity, dielectricparameters, elastic parameters) is urgently desired.

The invention has an object of providing media, in particular for MLC,IPS, TN or STN displays of this type, which do not have theabove-mentioned disadvantages or only do so to a reduced extent, andpreferably simultaneously have very high specific resistances and lowthreshold voltages. This object requires liquid-crystalline compoundswhich have a high clearing point and low rotational viscosity.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

It has now been found that these objects and others can be achieved ifthe liquid-crystalline compounds according to the invention are used.

The invention thus relates to liquid-crystalline compounds of theformula I

in which

-   R is H, an alkenyl radical having from 2 to 15 carbon atoms which is    unsubstituted, monosubstituted by CN or CF₃ or at least    monosubstituted by halogen, where, in addition, one or more CH₂    groups in these radicals may be replaced by —O—, —S—, —CH═CH—,    —C≡—C—, —OC—O— or —O—CO— in such a way that O atoms are not linked    directly to one another,-   A¹ and A² are each, independently of one another,    -   a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which        one or two non-adjacent CH₂ groups may be replaced by —O— or        —S—,    -   b) a 1,4-phenylene radical, in which one or two CH groups may be        replaced by N,    -   c) a radical from the group consisting of piperidine-1,4-diyl,        1,4-bicyclo[2.2.2]octylene, phenanthrene-2,7-diyl,        naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl,        1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl        and fluorene-2,7-diyl,    -   where the radicals a), b) and c) may be monosubstituted or        polysubstituted by halogen atoms,-   X is F, Cl, CN, NCS, SF₅, or a halogenated or unsubstituted alkyl,    alkoxy, alkenyloxy or alkenyl radical having up to 5 carbon atoms,-   Z¹ and Z² are each, independently of one another, —CO—O—, —O—CO—,    —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CH₂CH₂—, —(CH₂)₄—, —C₂F₄—,    —CH₂CF₂—, —CF₂CH₂—, —CF═CF—, —CH═CH—, —C≡C— or a single bond, with    the proviso that at least one of the bridges Z¹ and Z² is —CF₂O— or    —OCF₂—,-   a is 0, 1 or 2,-   b is 0, 1 or 2, and-   L¹, L² and L³ are each, independently of one another, H, F or Cl.

The invention furthermore relates to the use of the compounds of theformula I in liquid-crystalline media.

The compounds of the formula I have a broad range of applications.Depending on the choice of substituents, these compounds can serve asbase materials of which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or in order to optimize its thresholdvoltage and/or its viscosity.

In the pure state, the compounds of the formula I are colorless and formliquid-crystalline mesophases in a temperature range which is favorablylocated for electro-optical use. In particular, the compounds accordingto the invention are distinguished by their broad nematic phase range.In liquid-crystalline mixtures, the substances according to theinvention suppress the smectic phases and result in a clear improvementin the low-temperature storage stability. They are stable chemically,thermally and to light.

The invention relates in particular to the compounds of the formula I inwhich R is vinyl, CH₃CH═CH, CH₂═CHCH₂CH₂ or CH₃CH₂═CHCH₂CH₂.

Particular preference is given to compounds of the formula I in whicha=b=1 or a=b=2. Z¹ or Z² is preferably a single bond, furthermore—CF₂O—, —OCF₂—, —C₂F₄—, —CH₂O—, —OCH₂— or —COO—.

The alkenyl radical R may be straight-chain or branched. It ispreferably straight-chain and has from 2 to 10 carbon atoms.Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2-or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, 4- or-5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-,-5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, ordec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

If R is an alkenyl radical which is monosubstituted by CN or CF₃, thisradical is preferably straight-chain. The substitution by CN or CF₃ is,in any desired position.

If R is an alkenyl radical which is at least monosubstituted by halogen,this radical is preferably straight-chain, and halogen is preferably For Cl. In the case of polysubstitution, halogen is preferably F. Theresultant radicals also include perfluorinated radicals. In the case ofmonosubstitution, the fluorine or chlorine substituent may be in anydesired position, but is preferably in the ω-position.

Compounds of the formula I containing branched wing groups R mayoccasionally be of importance owing to better solubility in theconventional liquid-crystalline base materials, but in particular aschiral dopants if they are optically active. Smectic compounds of thistype are suitable as components of ferroelectric materials.

Compounds of the formula I having S_(A) phases are suitable forthermally addressed displays.

For reasons of simplicity, Cyc below denotes a 1,4-cyclohexyleneradical, Che denotes a 1,4-cyclohexenylene radical, Dio denotes a1,3-dioxane-2,5-diyl radical, Dit denotes a 1,3-dithiane-2,5-diylradical, Phe denotes a 1,4-phenylene radical, Pyd denotes apyridine-2,5-diyl radical, Pyr denotes a pyrimidine-2,5-diyl radical, Bidenotes a bicyclo[2.2.2]octylene radical, PheF denotes a 2- or3-fluoro-1,4-phenylene radical, PheFF denotes a 2,3-difluoro- or2,6-difluoro-1,4-phenylene radical, Nap denotes a substituted orunsubstituted naphthalene radical, Dec denotes a decahydronaphthaleneradical, and Phen denotes a substituted or unsubstituted phenanthreneradical.

For reasons of simplicity, A³—X below denotes

The compounds of the formula I accordingly include the preferredbicyclic compounds of the sub-formulae Ia to Ij:

(Z²=—CF₂O— or —OCF₂—):

R-Cyc-Z²-A³-X Ia R-Phe-Z²-A³-X Ib R-Pyr-Z²-A³-X Ic R-Dio-Z²-A³-X IdR-Bi-Z²-A³-X Ie R-PheF-Z²-A³-X If R-PheFF-Z²-A³-X Ig R-Nap-Z²-A³-X IhR-Dec-Z²-A³-X Ii R-Phen-Z²-A³-X IjThe compounds of the formula I accordingly include the preferredtricyclic compounds of the sub-formulae Ik to Iv:(Z¹ or Z²: —CF₂O— or —OCF₂—):

R-Cyc-Z¹-Cyc-Z²-A³-X Ik R-Cyc-Z¹-Phe-Z²-A³-X Il R-Cyc-Z¹-PheF-Z²-A³-X ImR-Cyc-Z¹-PheFF-Z²-A³-X In R-Phe-Z¹-Phe-Z²-A³-X Io R-Cyc-Z¹-Dio-Z²-A³-XIp R-Dio-Z¹-Cyc-Z²-A³-X Iq R-Dec-Z¹-Cyc-Z²-A³-X Ir R-Phe-Z¹-PheF-Z²-A³-XIs R-Phe-Z¹-PheFF-Z²-A³-X It R-Pyr-Z¹-Phe-Z²-A³-X IuR-Phe-Z¹-Phen-Z²-A³-X IvOf these, particular preference is given to the compounds of thesub-formulae Ia, Ib, Id, Ik, and II.

A¹ and A² are preferably Phe, PheF, PheFF, Cyc or Che, furthermore Pyror Dio, Dec or Nap. The compounds of the formula I preferably containnot more than one of the radicals Bi, Pyd, Pyr, Dio, Dit, Nap or Dec.

Preference is also given to all compounds of the formula I and of allsub-formulae in which A¹ and A² are a monosubstituted or disubstituted1,4-phenylene. These are, in particular, 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene and2,6-difluoro-1,4-phenylene.

Preferred subgeneric groups of compounds of the formula I are those ofthe sub-formulae I1 to I105:

wherein (F) means fluorine or hydrogen.

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works, such asHouben-Weyl, Methoden der organischen Chemie [Methods of OrganicChemistry], Georg-Thieme-Verlag, Stuttgart), to be precise underreaction conditions which are known and suitable for the said reactions.Use can also be made here of variants which are known per se, but arenot mentioned here in greater detail.

The compounds according to the invention can be prepared, for example,as follows:

The invention also relates to electro-optical displays (in particularSTN or MLC displays having two plane-parallel outer plates, which,together with a frame, form a cell, integrated non-linear elements forswitching individual pixels on the outer plates, and a nematicliquid-crystal mixture of positive dielectric anisotropy and highspecific resistance which is located in the cell) which contain media ofthis type, and to the use of these media for electro-optical purposes.

The liquid-crystal mixtures according to the invention enable asignificant widening of the available parameter latitude.

The achievable combinations of clearing point, viscosity at lowtemperature, thermal and UV stability and dielectric anisotropy are farsuperior to previous materials from the prior art.

The requirement for a high clearing point, a nematic phase at lowtemperature and a high Δε has hitherto only been achieved to aninadequate extent. Although liquid-crystal mixtures such as, forexample, MLC-6476 and MLC-6625 (Merck KGaA, Darmstadt, Germany) havecomparable clearing points and low-temperature stabilities, they have,however, relatively low Δn values and also higher threshold voltages ofabout ≧1.7 V.

Other mixture systems have comparable viscosities and Δ∈ values, butonly have clearing points in the region of 60° C.

The liquid-crystal mixtures according to the invention, while retainingthe nematic phase down to −20° C. and preferably down to −30° C.,particularly preferably down to −40° C., enable clearing points above80° C., preferably above 90° C., particularly preferably above 100° C.,simultaneously dielectric anisotropy values Δε of ≧4, preferably ≧6, anda high value for the specific resistance to be achieved, enablingexcellent STN and MLC displays to be obtained. In particular, themixtures are characterised by low operating voltages. The TN thresholdsare below 1.5 V, preferably below 1.3 V.

It goes without saying that, through a suitable choice of the componentsof the mixtures according to the invention, it is also possible forhigher clearing points (for example above 110°) to be achieved at ahigher threshold voltage or lower clearing points to be achieved atlower threshold voltages with retention of the other advantageousproperties. At viscosities correspondingly increased only slightly, itis likewise possible to obtain mixtures having greater Δε and thus lowerthresholds. The MLC displays according to the invention preferablyoperate at the first Gooch and Tarry transmission minimum [C. H. Goochand H. A. Tarry, Electron. Lett. 10, 2-4, 1974; C. H. Gooch and H. A.Tarry, Appl. Phys., Vol. 8,1575-1584, 1975] are used, where, besidesparticularly favorable electro-optical properties, such as, for example,high steepness of the characteristic line and low angle dependence ofthe contrast (German Patent 30 22 818), a lower dielectric anisotropy issufficient at the same threshold voltage as in an analogous display atthe second minimum. This enables significantly higher specificresistances to be achieved using the mixtures according to the inventionat the first minimum than in the case of mixtures comprising cyanocompounds. Through a suitable choice of the individual components andtheir proportions by weight, the person skilled in the art is able toset the birefringence necessary for a pre-specified layer thickness ofthe MLC display using simple routine methods.

The flow viscosity ν₂₀ at 20° C. is preferably <60 mm²·s⁻¹, particularlypreferably <50 mm²·s⁻¹. The nematic phase range is preferably at least90°, in particular at least 100°. This range preferably extends at leastfrom −30° to +80°.

Measurements of the capacity holding ratio (HR) [S. Matsumoto et al.,Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference,San Francisco, June 1984, p. 304 (1984); G. Weber et al., LiquidCrystals 5, 1381 (1989)] have shown that mixtures according to theinvention comprising compounds of the formula I exhibit a significantlysmaller decrease in the HR with increasing temperature than, forexample, analogous mixtures comprising cyanophenylcyclohexanes of theformula

or esters of the formula

instead of the compounds of the formula I.

The UV stability of the mixtures according to the invention is alsoconsiderably better, i.e. they exhibit a significantly smaller decreasein the HR on exposure to UV.

The media according to the invention are preferably based on a pluralityof (preferably two, three or more) compounds of the formula I, i.e. theproportion of these compounds is 5-95%, preferably 10-60% andparticularly preferably in the range 15-40%.

The individual compounds of the formulae I to IX and their sub-formulaewhich can be used in the media according to the invention are eitherknown or they can be prepared analogously to the known compounds.

Preferred embodiments are indicated below:

-   -   The medium preferably comprises one, two or three homologous        compounds of the formula I, where each homologue is present in        the mixture in a maximum proportion of 10%.    -   Medium additionally comprises one or more compounds selected        from the group consisting of the general formulae II to IX:

in which the individual radicals have the following meanings:

-   R⁰ is n-alkyl, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl, each    having up to 9 carbon atoms,-   X⁰ is F, Cl, halogenated alkyl, halogenated alkenyl, halogenated    alkenyloxy or halogenated alkoxy having up to 7 carbon atoms,-   Z⁰ is —CH═CH—, —C₂H₄—, —(CH₂)₄—, —C₂F₄—, —CF═CF—, —CF₂O—, —OCF₂— or    —COO—,-   Y¹, Y²,-   Y³ and Y⁴ are each, independently of one another, H or F, and-   r is 0 or 1.

The compound of the formula IV is preferably

-   -   The medium additionally comprises one or more compounds of the        formulae

in which R⁰ and Y² are as defined above.

-   -   The medium preferably comprises one, two or three, furthermore        four, homologues of the compounds selected from the group        consisting of H1 to H18 (n=1-7):

-   -   The medium additionally comprises one or more compounds selected        from the group consisting of the general formulae X to XV:

in which R⁰, X⁰, Y¹, Y², Y³ and Y⁴ are each, independently of oneanother, as defined in claim 7. X⁰ is preferably F, Cl, CF₃, OCF₃ orOCHF₂. R⁰ is preferably alkyl, oxaalkyl, fluoroalkyl, alkenyl oralkenyloxy.

-   -   The proportion of compounds of the formulae I to IX together in        the mixture as a whole is at least 50% by weight.    -   The proportion of compounds of the formula I in the mixture as a        whole is from 5 to 50% by weight.    -   The proportion of compounds of the formulae II to IX in the        mixture as a whole is from 30 to 70% by weight.

-   -   The medium comprises compounds of the formulae II, III, IV, V,        VI, VII, VII and/or IX.    -   R⁰ is straight-chain alkyl or alkenyl having from 2 to 7 carbon        atoms.    -   The medium essentially consists of compounds of the formulae I        to XV.    -   The medium comprises further compounds, preferably selected from        the following group consisting of the general formulae XVI to        XX:

in which R⁰ and X⁰ are as defined above, and the 1,4-phenylene rings maybe substituted by CN, chlorine or fluorine. The 1,4-phenylene rings arepreferably monosubstituted or polysubstituted by fluorine atoms.

-   -   The medium comprises further compounds, preferably selected from        the following group consisting of the formulae RI to RXI

in which

-   R⁰ is n-alkyl, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl, each    having up to 9 carbon atoms,-   d is 0, 1 or 2,-   Y¹ is H or F,-   alkyl and-   alkyl* are each, independently of one another, a straight-chain or    branched alkyl radical having 1-9 carbon atoms,-   alkenyl and-   alkenyl* are each, independently of one another, a straight-chain or    branched alkenyl radical having up to 9 carbon atoms.    -   The medium preferably comprises one or more compounds of the        formulae

in which n and m are each an integer from 1-9.

-   -   The I:(II+III+IV+V+VI+VII+VII+IX) weight ratio is preferably        from 1:10 to 10:1.    -   The medium essentially consists of compounds selected from the        group consisting of the general formulae I to XV.

It has been found that even a relatively small proportion of compoundsof the formula I mixed with conventional liquid-crystal materials, butin particular with one or more compounds of the formulae II, III, IV, V,VI, VII, VIII and/or IX, results in a significant lowering of thethreshold voltage and in low birefringence values, with broad nematicphases with low smectic-nematic transition temperatures being observedat the same time, improving the shelf life. The compounds of theformulae I to IX are colorless, stable and readily miscible with oneanother and with other liquid-crystalline materials.

The term “alkyl” or “alkyl*” covers straight-chain and branched alkylgroups having 1-9 carbon atoms, in particular the straight-chain groupsmethyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having2-5 carbon atoms are generally preferred.

The term “alkenyl” or “alkenyl*” covers straight-chain and branchedalkenyl groups having up to 9 carbon atoms, in particular thestraight-chain groups. Preferred alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples of particularly preferred alkenyl groups are vinyl,1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl,3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 carbon atoms are generally preferred.

The term “fluoroalkyl” preferably covers straight-chain groups having aterminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl,4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl.However, other positions of the fluorine are not excluded.

The term “oxaalkyl” preferably covers straight-chain radicals of theformula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and m are each,independently of one another, from 1 to 6. n is preferably=1 and m ispreferably from 1 to 6.

Through a suitable choice of the meanings of R⁰ and X⁰, the addressingtimes, the threshold voltage, the steepness of the transmissioncharacteristic lines, etc., can be modified in the desired manner. Forexample, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxyradicals and the like generally result in shorter addressing times,improved nematic tendencies and a higher ratio of the elastic constantsk₃₃ (bend) and k₁₁ (splay) compared with alkyl or alkoxy radicals.4-alkenyl radicals, 3-alkenyl radicals and the like generally give lowerthreshold voltages and smaller values of k₃₃/k₁₁ compared with alkyl andalkoxy radicals.

A —CH₂CH₂— group in Z¹ and/or Z² generally results in higher values ofk₃₃/k₁₁ compared with a single covalent bond. Higher values of k₃₃/k₁₁facilitate, for example, flatter transmission characteristic lines in TNcells with a 90° twist (in order to achieve grey shades) and steepertransmission characteristic lines in STN, SBE and OMI cells (greatermultiplexability), and vice versa.

The optimum mixing ratio of the compounds of the formulae I andII+III+IV+V+VI+VII+VIII+IX depends substantially on the desiredproperties, on the choice of the components of the formulae I, II, III,IV, V, VI, VII, VIII and/or IX, and the choice of any other componentsthat may be present. Suitable mixing ratios within the range given abovecan easily be determined from case to case.

The total amount of compounds of the formulae I to XV in the mixturesaccording to the invention is not crucial. The mixtures can thereforecomprise one or more further components for the purposes of optimisingvarious properties. However, the observed effect on the addressing timesand the threshold voltage is generally greater, the higher the totalconcentration of compounds of the formulae I to XV.

In a particularly preferred embodiment, the media according to theinvention comprise compounds of the formulae II to IX (preferably IIand/or III) in which X⁰ is OCF₃, OCHF₂, F, OCH═CF₂, OCF═CF₂, OCF₂CHFCF₃or OCF₂—CF₂H. A favorable synergistic effect with the compounds of theformula I results in particularly advantageous properties.

The construction of the MLC display according to the invention frompolarizers, electrode base plates and surface-treated electrodescorresponds to the conventional construction for displays of this type.The term “conventional construction” is broadly drawn here and alsocovers all derivatives and modifications of the MLC display, inparticular including matrix display elements based on poly-Si TFT orMIM.

A significant difference between the displays according to the inventionand the conventional displays based on the twisted nematic cellconsists, however, in the choice of the liquid-crystal parameters of theliquid-crystal layer.

The liquid-crystal mixtures which can be used in accordance with theinvention are prepared in a manner conventional per se. In general, thedesired amount of the components used in the lesser amount is dissolvedin the components making up the principal constituent, advantageously atelevated temperature. It is also possible to mix solutions of thecomponents in an organic solvent, for example in acetone, chloroform ormethanol, and to remove the solvent again, for example by distillation,after thorough mixing.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature, such as, forexample, stabilisers and antioxidants. For example, 0-15% of pleochroicdyes or chiral dopants can be added.

C denotes a crystalline phase, S a smectic phase, S_(C) a smectic Cphase, S_(B) a smectic B phase, N a nematic phase and I the isotropicphase.

V₁₀ denotes the voltage for 10% transmission (viewing angleperpendicular to the plate surface). t_(on) denotes the switch-on timeand t_(off) the switch-off time at an operating voltage corresponding to2 times the value of V₁₀. Δn denotes the optical anisotropy and n₀ therefractive index. Δε denotes the dielectric anisotropy (Δε=ε_(∥)−ε_(⊥),where ε_(∥) denotes the dielectric constant parallel to the longitudinalmolecular axes and ε_(⊥) denotes the dielectric constant perpendicularthereto). The electro-optical data were measured in a TN cell at the 1st minimum (i.e. at a d·Δn value of 0.5) at 20° C., unless expresslystated otherwise. The optical data were measured at 20° C., unlessexpressly stated otherwise.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding German application No. 10148356.2,filed Sep. 29, 2001 are incorporated by reference herein.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the following examples, all temperatures are setforth uncorrected in degrees Celsius and, all parts and percentages areby weight, unless otherwise indicated.

EXAMPLES

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetransformation into chemical formulae taking place in accordance withTables A and B below. All radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) arestraight-chain alkyl radicals having n and m carbon atoms respectively;n and m are in each case, independently of one another, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. The coding in Table B isself-evident. In Table A, only the acronym for the parent structure isindicated. In individual cases, the acronym for the parent structure isfollowed, separated by a dash, by a code for the substituents R¹, R², L¹and L²:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) HH n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN H F nF C_(n)H_(2n+1) F HH nOF OC_(n)H_(2n+1) F H H nCl C_(n)H_(2n+1) Cl H H nF.F C_(n)H_(2n+1) FH F nF.F.F C_(n)H_(2n+1) F F F nCF₃ C_(n)H_(2n+1) CF₃ H H nOCF₃C_(n)H_(2n+1) OCF₃ H H nOCF₂ C_(n)H_(2n+1) OCHF₂ H H nS C_(n)H_(2n+1)NCS H H rVsN C_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H rEsNC_(r)H_(2r+1)—O—C₂H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) H HnOCCF₂.F.F C_(n)H_(2n+1) OCH₂CF₂H F F

Preferred mixture components are shown in Tables A and B.

TABLE A

PYP

PYRP

BCH

CBC

CCH

CCP

CPTP

CEPTP

ECCP

CECP

EPCH

PCH

PTP

BECH

EBCH

CPC

B

FET-nF

CGG

CGU

CUP

CCQU

PGU

TABLE B

CBC-nmF

PCH-nOm FET-nCl

CP-nOCF₃

CCH-nOm BCH-n.FX

Inm

CBC-nmF

ECCP-nm CCH-n1EM

T-nFm CGU-n-F

CCP-nOCF₃.F CGG-n-F

CCP-nOCF₂.F(.F) CCP-nF.F.F

CGU-n-OXF

CUZU-n-F CGU-n-O1DT

CGU-n-O1DT CC-n-V1

CC-n-V CCP-nOCF₃

BCH-nF.F.F

CWCZU-n-F

CWCZG-n-F

CCOC-n-m

CGZU-n-F CUZP-n-F

CGU-1V-F CCG-V-F

CGZP-n-F UZP-n-N

CGZP-n-OT

CUZP-n-OT

CCQU-n-F Dec-U-n-F

Nap-U-n-F

CQGZP-n-F

CCQP-n-S

CPUQU-n-F

CCEEU-n-F CEECU-n-F

CCQU-V-F CCQU-1V-F

PUQU-V2-F

TABLE C Table C shows possible dopants which are generally added to themixtures according to the invention.

C 15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

CN

R/S-4011

R/S-2011

TABLE D Stabilisers which can be added, for example, to the mixturesaccording to the invention are mentioned below.

The following examples are intended to explain the invention withoutrestricting it. Above and below, percentages are per cent by weight. Alltemperatures are given in degrees Celsius. m.p. denotes melting point,cl.p. denotes clearing point. Furthermore, C=crystalline state,N=nematic phase, S=smectic phase and I=isotropic phase. The data betweenthese symbols represent the transition temperatures. Δn denotes opticalanisotropy (589 nm, 20° C.), the flow viscosity ν₂₀ ((mm²/sec) wasdetermined at 20° C. The rotational viscosity γ₁ [mPa·s] was likewisedetermined at 20° C.

“Conventional work-up” means that water is added if necessary, themixture is extracted with dichoromethane, diethyl ether, methyltert-butyl ether or toluene, the phases are separated, the organic phaseis dried and evaporated, and the product is purified by distillationunder reduced pressure or crystallisation and/or chromatography. Thefollowing abbreviations are used:

n-BuLi 1.6 molar solution of n-butyllithium in n-hexane DMAP4-(dimethylamino)pyridine THF tetrahydrofuran DCCN,N′-dicyclohexylcarbodiimide LDA lithium dimethylamide

Example 1

0.780 mol of B in 2.5 l of abs. THF are initially introduced and cooledto −70° C. At −70° C., 0.780 mol of n-BuLi (15% solution in n-hexane) isadded dropwise, and the mixture is stirred at −70° C. for 0.5 hour andwarmed slowly to −15° C. After 0.78 mol of A has been added at −70° C.,the mixture is stirred overnight at room temperature. Methyl tert-butylether and NaHCO₃ solution are added to the mixture, which is subjectedto conventional work-up. The crude product is recrystallised fromn-heptane.

0.1 mol of C is dissolved in 300 ml of dichloromethane, and 0.1 mol oftrifluoromethanesulfonic acid is added with ice cooling. The reactionmixture is stirred at 5° C., allowed to warm to room temperature andstirred for a further 2 hours. A mixture of 0.15 mol of3,4,5-trifluorophenol and 0.18 mol of triethylamine in 30 ml ofdichloromethane is added dropwise to the reaction mixture at −70° C.,and the mixture is subsequently stirred at −70° C. for 1 hour. After 0.5mol of triethylamine trishydrofluoride has been added, a mixture of1,3-dibromo-5,5-dimethylhydantoin in 170 ml of dichloromethane is addedin portions. The mixture is stirred at −70° C. for a further 1 hour, and300 ml of a 1 molar NaOH solution are added at −20° C. The aqueous phaseis separated off and extracted with dichloromethane. The combinedorganic phases are subjected to conventional work-up.

200 ml of formic acid are added to 0.083 mol of D dissolved in 250 ml ofabs. toluene, and the mixture is stirred overnight at room temperature.The formic acid is separated off and extracted with toluene. Thecombined organic phases are subjected to conventional work-up. Theresidue is recrystallised from n-heptane.

0.013 mol of E and 0.019 mol of methoxymethyltriphenylphosphoniumchloride in 300 ml of abs. THF are introduced into an inert apparatusand cooled at −5° C. After 0.019 mol of potassium tert-butoxide in 50 mlof abs. THF has been added, the mixture is stirred at 0° C. for 1 hourand at room temperature overnight. After H₂O and a few drops of diluteHCl have been added, the organic phase is separated off and subjected toconventional work-up.

200 ml of formic acid are added to 0.083 mol of F dissolved in 250 ml ofabs. toluene, and the mixture is stirred overnight at room temperature.The formic acid is separated off and extracted with toluene. Thecombined organic phases are subjected to conventional work-up. Theresidue is recrystallised from n-heptane.

2.82 mmol of G and 3.36 mmol of methyltriphenylphosphonium bromide aredissolved in 40 ml of abs. THF and cooled to 2° C. 3.36 mmol ofpotassium tert-butoxide in 20 ml of abs. THF are added dropwise to thissolution and dissolved overnight at room temperature. Thetriphenylphosphine oxide is filtered off with suction, and the filtrateis evaporated to dryness. The crude product, dissolved in n-heptane, isfiltered through a silica frit, and the filtrate is re-evaporated. Theresidue is recrystallised from n-pentane at −20° C. C, 29; N, 88.4; I;Δn=0.0761; Δε=8.3.

The following compounds of the formula

are prepared analogously:

X L¹ L² F H H F F H OCF₃ H H OCF₃ F H OCF₃ F F OCH₂CF₃ H H OCH₂CF₃ F HOCH₂CF₃ F F Cl H H Cl F H Cl F F CN H H CN F H CN F F SF₅ H H SF₅ F HSF₅ F F NCS H H NCS F H NCS F F OCHF₂ H H OCHF₂ F H OOHF₂ F F CF₃ H HCF₃ F H CF₃ F F OCF₂CHFCF₃ H H OCF₂CHFCF₃ F H OCF₂CHFCF₃ F F OC₃F₇ H HOC₃F₇ F H OC₃F₇ F F C₃F₇ H H C₃F₇ F H C₃F₇ F F

Mixture Examples Example M1

BCH-3F.F 10.80% Clearing point [° C.]: 90.3 BCH-5F.F 9.00% Δn [589 nm,20° C.]: 0.0945 ECCP-30CF₃ 4.50% Δε [1 kHz, 20° C.]: 5.6 ECCP-50CF₃4.50% CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.20% PCH-7F5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.80% CCP-40CF₃ 6.30% CCP-50CF₃ 9.90%PCH-5F 9.00% CCQU-V-F 10.00%

Example M2

CCP-2F.F.F 12.00% Clearing point [° C.]: 76 CCP-3F.F.F 10.00% Δn [589nm, 20° C.]: 0.0916 CCP-5F.F.F 1.00% V_(10,0,20): 1.23 CCP-20CF₃ 8.00%γ₁: 152 CCP-30CF₃ 8.00% CCP-40CF₃ 7.00% CCP-50CF₃ 7.00% CGU-2-F 12.00%CGU-3-F 10.00% CGU-5-F 10.00% CCQU-V-F 15.00%

Example M3

CCP-2F.F.F 12.00% Clearing point [° C.]: 75.7 CCP-3F.F.F 10.00% Δn [589nm, 20° C.]: 0.0928 CCP-5F.F.F 6.00% V_(10,0,20): 1.18 CCP-20CF₂.F.F1.00% γ₁: 146 CCP-20CF₃ 8.00% CCP-30CF₃ 8.00% CCP-40CF₃ 7.00% CGU-2-F12.00% CGU-3-F 10.00% CWCQU-2-F 5.50% PGU-2-F 5.50% CCQU-V-F 15.00%

Example M4

CCP-2F.F.F 12.00% Clearing point [° C.]: 75 CCP-3F.F.F 10.00% Δn [589nm, 20° C.]: 0.0932 CCP-20CF₃ 8.00% V_(10,0,20): 1.17 CCP-30CF₃ 8.00%γ₁: 139 CCP-40CF₃ 7.00% CCP-50CF₃ 4.00% CGU-2-F 12.00% CGU-3-F 4.00%CCQU-2-F 12.00% PGU-2-F 8.00% CCQU-V-F 15.00%

Example M5

CCP-2F.F.F 12.00% Clearing point [° C.]: 76 CCP-3F.F.F 2.50% Δn [589 nm,20° C.]: 0.0930 CCP-20CF₃ 8.00% V_(10,20): 1.20 CCP-30CF₃ 8.00% γ₁: 137CCP-40CF₃ 7.00% CCP-50CF₃ 3.00% CGU-2-F 12.00% CGU-3-F 10.00% CCP-2F.F9.00% CCP-3F.F 6.00% PGU-2-F 6.50% CCGU-3-F 1.00% CCQU-V-F 15.00%

Example M6

BCH-3F.F 10.80% Clearing point [° C.]: 81.7 BCH-5F.F 9.00% Δn [589 nm,20° C.]: 0.0996 ECCP-30CF₃ 4.50% Δε [1 kHz, 20° C.]: 6.5 ECCP-50CF₃4.50% d*Δn [nm]: 0.5 CBC-33F 1.80% Twist: 90 CBC-53F 1.80% CBC-55F 1.80%PCH-6F 7.20% PCH-7F 5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.80% CCP-40CF₃6.30% CCP-50CF₃ 9.90% PCH-5F 9.00% PUQU-V2-F 10.00%

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A liquid-crystalline medium comprising at least two mesogenic compounds: wherein the medium contains substantially no compounds having a cyano group; wherein at least one mesogenic compound is a compound of the formula I

in which R is vinyl, CH₃CH═CH—, CH₂═CHCH₂CH₂— or CH₃CH═CHCH₂CH₂—, A¹ and A² are each, independently of one another, a) a 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH₂ groups are optionally replaced by —O— or —S—, b) a 1,4-phenylene radical, in which one or two CH groups are optionally replaced by N, c) a radical selected from the group consisting of piperidine-1,4-diyl, 1,4-bicyclo[2.2.2]octylene, phenanthrene-2,7-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl, where the radicals a), b) and c) are optionally mono-to perhalo-substituted by halogen atoms, X is F, Cl, NCS, SF₅, or a halogenated or unsubstituted alkyl, alkoxy, alkenyloxy or alkenyl radical having 1 to 5 carbon atoms, Z¹ and Z² are each, independently of one another, —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CH₂CH₂—, —(CH₂)₄—, —C₂F₄—, —CH₂CF₂—, —CF₂CH₂—, —CF═CF—, —CH═CH—, —C≡C— or a single bond, a is 0, 1 or 2, b is 0, 1 or 2, provided that a and b are not both 0 and that the compound contains at least one bridge Z¹ or Z² which is —CF₂O— or —OCF₂—, and L¹, L² and L³ are each, independently of one another, H, F, or Cl; and wherein at least one other mesogenic compound is a compound of one of formulae II to IX:

in which: R⁰ is n-alkyl, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl, each having 1 to 9 carbon atoms, X⁰ is halogenated alkoxy having 1 to 7 carbon atoms, Z⁰ is —CH═CH—, —C₂H₄—, —(CH₂)₄—, —C₂F₄—, —CF═CF—, —CF₂O—, —OCF₂— or —COO—, Y¹, Y², Y³ and Y⁴ are each, independently of one another, H or F, and r is 0 or 1, provided that the variables are selected such that the compounds of formulae IV, V and VII do not include compounds within the scope of formula I; and provided that the medium does not contain: a compound of the formula II

wherein R⁰ is alkenyl and r is 1, a compound of the formula IV

where R⁰ is alkenyl, Z⁰ is a single bond and r is 1, or a compound of any of formulae RI—RV or RIX—RX:

where R⁰ is alkenyl alkyl* are each, independently of one another, a straight-chain or branched alkyl radical having 1-9 carbon atoms, alkenyl and alkenyl* are each, independently of one another, a straight-chain or branched alkenyl radical having up to 9 carbon atoms and d is 0, 1 or
 2. 2. A liquid-crystalline medium according to claim 1, wherein in formula I, a+b=1 or a+b=2.
 3. A liquid-crystalline medium according to claim 1, wherein in formula I, L¹ is fluorine and L² is fluorine or hydrogen.
 4. A liquid-crystalline medium according to claim 1, wherein in formula I, L² and L³ are fluorine.
 5. A liquid-crystalline medium according to claim 1, wherein the compound of formula I is of one of the formulae I1 to I105:

in which R and X are as defined in claim 1 and (F) means fluorine or hydrogen.
 6. An electro-optical liquid-crystal display which comprises a liquid-crystalline medium according to claim
 1. 7. A medium of claim 1, wherein, in formula I, A¹ and A² are independently selected from Phe, PheF, PheFF, Cyc, Che, Pyr, Dio, Dec or Nap, provided that the compound does not contain more than one of Pyr, Dio, Dec, or Nap, where Cyc denotes a 1,4-cyclohexylene radical, Che denotes a 1,4-cyclohexenylene radical, Dio denotes a 1,3-dioxane-2,5-diyl radical, Phe denotes a 1,4-phenylene radical, Pyr denotes a pyrimidine-2,5-diyl radical, PheF denotes a 2- or 3-fluoro-1,4-phenylene radical, PheFF denotes a 2,3-difluoro- or 2,6-difluoro-1,4-phenylene radical, Nap denotes a substituted or unsubstituted naphthalene radical, and Dec denotes a decahydronaphthalene radical.
 8. A medium of claim 1, wherein, in formula I, A¹ and A² are independently selected from monofluoro-substituted or difluoro-substituted 1,4-phenylene.
 9. A liquid-crystalline medium of claim 1, wherein the medium has a nematic phase down to −20° C., a clearing point above 80° C., and a dielectric anisotropy, Δε, of ≧4.
 10. A liquid-crystalline medium of claim 9, wherein the medium has a TN threshold below 1.5 V.
 11. A liquid-crystalline medium of claim 1, wherein the medium contains 5-95% by weight of compounds of the formula I.
 12. A liquid-crystalline medium of claim 1, wherein the medium contains 10-60% by weight of compounds of the formula I.
 13. A liquid-crystalline medium of claim 1, wherein the medium comprises at least one compound of one of the formulae II to IX wherein X⁰ is —OCF₃.
 14. A liquid-crystalline medium of claim 1, wherein the medium comprises at least one compound of the formula II or III.
 15. A liquid-crystalline medium of claim 1, wherein the medium has a clearing point above 75° C.
 16. A liquid-crystalline medium of claim 1, wherein the medium has a flow viscosity, ν₂₀, at 20° C., of <60 mm²·s⁻¹.
 17. A liquid-crystalline medium of claim 1, wherein the medium has a rotational viscosity, γ₁, at 20° C., of 152 mPa·s or less. 